1. Field of the Invention
The present invention relates to methods and compositions for pest or pathogen control in plants. More particularly, it discloses transgenic plant cells, plants and seeds comprising recombinant DNA and methods of making and using such plant cells, plants and seeds that are associated with pest resistance.
2. Description of Related Art
Plants and animals are targets for infection by many nematode pests. Improved methods for protecting plants from nematode infection are therefore desired since they would increase the amount and stability of food production.
There are numerous plant-parasitic nematode species, including various cyst nematodes (e.g. Heterodera spp.), root knot nematodes (e.g. Meloidogyne spp.), lesion nematodes (e.g. Pratylenchus spp.), dagger nematodes (e.g. Xiphinema spp.) and stem and bulb nematodes (e.g. Ditylenchus spp.), among others. Tylenchid nematodes (members of the order Tylenchida), including the families Heteroderidae, Meloidogynidae, and Pratylenchidae, are the largest and most economically important group of plant-parasitic nematodes. Other important plant-parasitic nematodes include Dorylaimid nematodes (e.g. Xiphinema spp.), among others. Nematode species grow through a series of lifecycle stages and molts. Typically, there are five stages and four molts: egg stage; J1 (i.e. first juvenile stage); M1 (i.e. first molt); J2 (second juvenile stage; sometimes hatch from egg); M2; J3; M3; J4; M4; A (adult). Juvenile (“J”) stages are also sometimes referred to as larval (“L”) stages. Gene expression may be specific to one or more lifecycle stages. Nematodes have evolved as very successful parasites of both plants and animals and are responsible for significant economic losses in agriculture and livestock and for morbidity and mortality in humans. Nematode parasites of plants can inhabit all parts of plants, including roots, developing flower buds, leaves, and stems. Plant parasites are classified on the basis of their feeding habits into the broad categories migratory ectoparasites, migratory endoparasites, and sedentary endoparasites. Sedentary endoparasites, which include the root knot nematodes (Meloidogyne species, RKN), cyst nematodes (Globodera and Heterodera species) and reniform nematodes (Rotylenchulus species) induce feeding sites and establish long-term infections within roots that are often very damaging to crops. Nematode infection is a significant problem in the farming of many agriculturally significant crops. For example, soybean cyst nematode (Heterodera glycines, SCN) is believed to be responsible for yield losses in soybeans estimated to be in excess of $1 billion per year in North America. Such damage is the result of the stunting of the soybean plant caused by the cyst nematode. The stunted plants have smaller root systems, show symptoms of mineral deficiencies in their leaves, and wilt easily. It is estimated that parasitic nematodes cost the horticulture and agriculture industries in excess of $78 billion worldwide a year, based on an estimated average 12 percent annual loss spread across all major crops.
Traditional approaches for control of plant diseases have been the use of chemical treatment and the construction of interspecific hybrids between resistant crops and their wild-type relatives as sources of resistant germplasm. Chemical nematode control agents are not effective in eradicating nematode infestations. Because of the lack of selectivity, the chemical nematode control agents exert their effects on non-target fauna as well, often effectively sterilizing a field for a period of time following the application of nematode control agents. Nematicides such as Aldicarb and its environmental breakdown products are known to be highly toxic to mammals. As a result, government restrictions have been imposed on the use of these chemicals. The most widely used nematicide, methyl bromide, is scheduled to be soon retired from use, and at present, there is no promising candidate to replace this treatment.
Methods employing plant biotechnology have provided effective means to control insect infestations, for instance through plant expression of an insect control agent. Biotechnologically-related nematode control agents have generally been reported to be nucleotides expressed by a plant that are selectively toxic to the target nematode when ingested by the nematode. However, there are few examples of effectively applied biotechnology methods to control nematode infection.